Many engines have already been designed to that end. There are thus well-known spark-ignition four-stroke engines with four valves per cylinder, a spark plug situated in the cylinder with the cylinder head on the longitudinal axis of the cylinder having intake pipes positioned running substantially parallel to the axis of the cylinder, and into which the fuel-injection nozzle opens just below the intake valves.
The piston associated with these engines commonly has a specific hollow intended to channel the injection nozzle jet and to intensify the motion of the gases in the combustion chamber.
There are also well-known engines whose piston has a spherical bowl (or hollow) situated, at the top dead center, just opposite the fuel-injection nozzle and the spark plug. Patent application EP-A1-0,558,072 describes an engine with this characteristic.
All these engines have large capacities (cylinder bores above 80 mm) and they commonly have four valves per cylinder.
There are also well-known engines of the same type but with three valves per cylinder. Patent application EN.97/06,731 filed in the name of the applicant illustrates a particular example of such engines.
They allow combustion in a stratified mode at low loads and/or so-called homogeneous combustion at high loads.
The combustion is referred to as stratified when a zone of the combustion chamber contains a richer mixture than the rest of the chamber, at low loads. This allows easier ignition of the mixture since the fuel-enriched zone is globally close to the spark plug.
At high loads, so-called homogeneous combustion is recommended. The mixture then has to be very homogeneous in the whole of the combustion chamber.
Direct injection engines currently work properly either in one mode or in the other. It is generally difficult to reconcile both operating modes.